Vinyl halide polymers and imidazolinemetal compound-epoxy curing systems therefor



United States Patent VINYL HALIDE POLYMERS AND IMIDAZOLINE- METALCOMPOUND-EPQXY CURING SYSTEMS THEREFGR Philip K. lisaacs, Brookline,Elizabeth C. Dearborn,

Boston, and Melvin Nimoy, Hyde Park, Mass., assignors to W. R. Grace &(10., Cambridge, Mass., a corporation of Qonnecticut No Drawing. FiledGet. 11, 1960, Ser. No. 61,825 12 Claims. (Cl. 26tl23) The inventionrelates to plastic compositions having desirable thermosetting andadhesive characteristics. In a particular aspect it relates to polymersand copolymers of vinyl chloride.

Vinyl polymers are versatile materials responding to many uses and areavailable in plasticized or unplasticized form. The unplasticized orrigid resins are prepared to take maximum advantage of their excellentchemical resistance. Most uses, however, require modification of thepolymers by the addition of plasticizers, fillers, and pigments to givethem desirable properties for specific commercial applications and forprocessing. Plasticizers play an important role in modifying theseresins to meet a wide variety of requirements.

Modification of the original polymer by the addition of processing aidsor other additives frequently adversely affects its chemical resistance.Polyvinyl chloride, in general, requires a large amount of plasticizerfor most applications. In use the excess plasticizer tends to migrate tothe surface and consequently impairs the adhesive properties of thepolymer. In addition, these polymers are thermoplastic which prohibitstheir use at high temperatures.

It is, therefore, an object of this invention to provide improved vinylhalide polymer compositions which are thermosetting in nature and adherewell to many surfaces. The improved compositions comprise a halogencontaining polymeric material, an imidazoline curing agent, a metalliccompound which regulates the curing action of the imidazoline, and anepoxy compound which together with the other components, providesincreased adhesion, thermal stability and crosslinking of the polymer.In addition, fillers, dyes, pigments and other additives may beincorporated in the compositions depending on the use to which they areput. They may be processed by extrusion, calendering, molding, plastisolor organosol application or other standard fabricating techniques.

Imidazolines are highly effective curing agents for halogenatedpolymers. The use of these imidazolines alone, however, has definitedisadvantages when added to certain vinyl polymer systems, such as pastegrade polyvinyl chloride plasticized with dioctyl phthalate. One, isthat the shelf life of the resulting plastisol is greatly reduced. Ineffect, the imidazoline solvates the polyvinyl chloride particles so asto produce a gel instead of a fluid after storing for several days atroom temperature. The second disadvantage is that the product blackens,stiffens and evolves HCl on heating, and it is difiicult to obtain ahigh degree of crosslinking without encountering these signs ofdegradation. This invention provides a means of preventing these twoside effects while maintaining the advantages of imidazoline cure. Inaddition, solvent resistance is improved coupled with increasedcrosslinking while at the same time imparting adhesive properties to thepolymeric material.

The imidazolines most useful in the practice of the in- "ice vention maybe defined as 2-substituted-Z-imidazoline andl,2-disubstituted-Z-imidazoline having the structure:

N@ @CH:

Where R represents an aliphatic group containing 1 to 36 carbon atomsand R may be hydrogen, or the group Where R may be hydrogen, hydroxyl,NH or a chain containing aliphatic ester groups, other 2-substituted-2-imidazoline or 1,2-disubstituted-Z-imidazoline groups, aliphatic amidogroups, aliphatic amino groups or a combination of such groups. Thisdefinition is intended to include as equivalents such compounds whereeither or both of the 4 or 5 carbon atoms on the imidazoline ring aresubstituted with a lower alkyl group such as methyl or ethyl.

The imidazolines may be prepared by reacting alkylene diamines havingamino groups on adjacent carbon atoms or polyalkylene polyamines withmonoor dicarboxylic acids under reactive conditions of temperature andpressure. Suitable amines include ethylene and propylene diamine,diethylene and dipropylene triamine, triethylene tetramine andtetraethylene pentamine. Representative monocarboxylic acids are acetic,caproic, pelargonic, laurie, palmitic, oleic and stearic acids. Typicaldicarboxylic acids include dimerized fatty acids, adipic, pimelic,suberic, azelaic and sebacic acids.

The preferred imidazolines are those which in themselves arenon-volatile and chemically stable at curing temperatures. In addition,they should be such that the uncured mixture with halogen containingpolymer undergoes no change with time at room temperature. The lowmolecular weight imidazolines, such as lysidine, are effective curingagents but tend to form fumes at curing temperatures and hydrolyze atroom temperature when exposed to moist air. Other imidazolines, such asoctamethylene diimidazoline, are high melting crystalline solids thatare difficult to incorporate uniformly in the polymer composition andhave limited compatibility with some halogen containing polymers. Themost useful of the imidazoline structures from these points of view arethe reaction products of fat-derived acids with diethylene triamine andits homologues.

The class of metallic compounds which are operable in this invention arethe oxides, sulfides and salts of metals of group HE and IVA of theperiodic table of elements. The specific metals are zinc, cadmium,mercury and lead and the compounds of these metals are limited to thosewhich are soluble in ammonium salts or ammonia solutions and formammonia complexes. The metallic compounds should preferably be in afinely divided state so as to present adequate surface for reaction anda particle size of about .5 micron or less has been found effective.While certain metal compounds will perform one or two of the threedesirable functions, i.e., delayed blackening, better adhesion or lessexudation, such materials do not fall in the operable general classdescribed above.

There are a vast number of epoxy compounds which may be used in thepractice of this invention. One group embraces the epoxidizedtriglycerides of vegetable and marine oil fatty acids. The vegetableoils include epoxidized castor, corn, hempseed, mustard seed, olive,peanut, poppy seed, soybean, tung and walnut oils. The marine oilsinclude epoxidized cod liver, hering, menhaden, California sardine(pilchard), Japanese sardine, gray seal and whale oils.

Another group of epoxy compounds includes epoxidized esters of ethenoidalcohols with carboxylic acids. Typical alcohols include themonoethenoid monohydroxy alcohols, such as crotyl alcohol(2-buten-l-ol), oleyl alcohol, citronellol, cinnamyl alcohol and methyltetrahydrobenzyl alcohol. Representative acids include themonocarboxylic and polycarboxylic acids such as acetic, caproic,pelargonic, lauric, palmitic, stearic, lignoceric, glutaric, adipic,pimelic, suberic, azelaic, phthalic and sebacic acid. Exemplaryepoxidized esters falling within this group include 2,3-epoxybutylacetate, 2,3-epoxybutyl caproate, 2,3-epoxybutyl palmitate, di(2,3epoxybutyl) adipate, di(2,3-epoxybutyl)-sebacate, 2,3-epoxycinnarnyllaurate, di(2,3-epoxycinnamyl)-adipate and di(2,3-epoxybutyl) phthalate.

A further group of epoxy compounds includes epoxidized esters ofmonohydroxy and polyhydroxy alcohols and ethenoid carboxylic acids.Appropriate alcohols include methanol, ethanol, butanol, pentanol,octanol, hexadecanol, cyclopentanol, cyclohexanol, benzyl alcohol,ethylene glycol, propylene glycol, hexamethylene glycol, glycerol andtrimethylolpropane. Suitable acids include: the monoethenoidmonocarboxylic fatty acids, such as obtusilic, lauroleic, palmitoleic,oleic, elaidic and erucic acid; the polyethenoid monocarboxylic fattyacids, such as sorbic linoleic, hiragonic, linolenic, moroctic,arachidonic and methyl tetrahydrobenzoic acid; and the substitutedmonoand polyethenoid monocarboxylic acids, such as ricinoleic andlicanic acid. Monoethenoid dicarboxylic acids include maleic, fumaric,itaconic and aconitic acid. Representative epoxidized esters fallingunder this group include lower alkyl 9,10-epoxy-stearate; hexadecyl9,10-epoxy-stearate; cyclopentyl 9,10-epoxystearate; cyclohexyl9,10-epoxystearate; butyl 9,10,12,13- diepoxystearate; octyl9,l0,12,13-diepoxystearate; butyl 9,10-epoxypalmitate; butyl9,l0,12,l3,15,16-triepoxystearate; butyl 12-hydroxy-9,10-epoxystearate;butyl 12-acetoxy-9,10-epoxystearate and methyl epoxy tetrahydrobenzylmethyl epoxy tetrahydrobenzoate.

Still another group of epoxy compounds which are useful in thisinvention includes the epoxidized esters of ethenoid alcohols andethenoid carboxylic acids. Suitable alcohols include the monoethenoidmonohydroxy alcohols, such as crotyl, oleyl, citronellol and cinnamylalcohol. Typical acids include: the monoethenoid monocarboxylic fattyacids, such as lauroleic, palmitoleic, oleic, elaidac and erucic acid;the polyethenoid monocarboxylic 4 9,10,12,13,15,16-triepoxystearate;2,3-epoxybutyl l2 hydroxy-9,l0-epoxystearate; 2,3-epoxybutyl 12 acetoxy-9,10-epoxystearate; 2,3 epoxycinnamyl-9,IO-epoxypalmitate;2,3-epoxycinnamyl-9,10,12,13-diepoxystearate; 2,3-epoxybutyl-Z,3-epoxysuccinate; and di(2,3 epoxybutyl)-2,3-epoxyoctanoate.

Another group comprises epoxidized olefins, diolefins and polyolefins,such as epoxidized 2-butene, 2-pentene, 2-methyl-2-butene,Z-methyl-Z-pentene, 2,4-hexadicne, cyclobutene, cyclopentene,cyclohexene, cyclooctene, cyclopentadiene, and polybutadiene.

Epoxidation of the ethenoid compounds is readily obtained by use oftypical epoxidzing agents such as peracetic acid, performic acid, orhydrogen peroxide. The epoxy groups in these compounds occupy aninternal position at least one carbon atom away from any terminal pointon the molecule chain.

The metal and epoxy compounds regulate the curing action of imidazolineson polyvinyl halides and produce unexpected improvements in theproperties of the polymer. These materials have a very specific actionon polyvinyl halide-imidazoline combinations compared to any otherinorganic additive. They simultaneously retard blackening on heating,prevent gas evolution, improve adhesion to many surfaces, and augmentresistance of the adhesive bond to water. Their action on polyvinylchloride, for example, is entirely different from the well knownstabilizing action of metal soaps. Many materials which perform well inthe present system will accelerate the degradation of unvulcanizedpolyvinyl chloride compositions. Contrariwise, materials which normallycontrol polyvinyl chloride degradation have no effect in this system.Another aspect of this invention is the plural function of the epoxycompound. On one hand, it provides the soft consistency needed for manyapplications and, on the other, it promotes infusibility andinsolubility by increasing the number of crosslinkages which we believeto be in the order of about one per 10,000 to one per 500 molecularweight units.

The invention is further illustrated by the following examples.Proportions here and elsewhere herein are expressed as parts orpercentages by weight. To simplify the presentation we have depictedwhat We believe to be the structure of the particular imidazolines usedin the examples and they are reproduced and designated as follows:

Imidazoline 1 One mole of sebacic acid, 2 moles of triethylene tetramineand 1 mole of oleic acid were reacted, resulting in a loss of 6 moles ofwater. The reaction was carried out for 4 hours at 150 C.220 C. at760-15 mm. of pressure in an atmosphere of nitrogen. The reactants werevigorously stirred throughout the reaction period. The product was amixture of imidazolines in which the following structure waspredominant:

N CH:

O 2 acids, such as sorbic, linoleic, hiragonic, linolenic, moroctic andarachidonic and; the substituted monoand polyethenoid monocarboxylicacids, such as ricinoleic and licanic acid; and the monoethenoidpolycarboxylic acids, such as maleic, fumaric, itaconic, aconitic and 2-octenedioc acid. Illustrative epoxidized esters which are classifiedunder this group include 2,3-epoxybutyl-9,10-

epoxypalmitate; 2,3 epoxybuty1-9,10-epoxystearate; 2,3-epoxybutyl-9,10,12,13-diepoxystearate; 2,3 epoxybutyl- N CH;

N CH;

Imidazoline II lmidazoline III This compound was prepared by reactingequimolar amounts of acetic acid and triethylene tetramine for 4 hoursat 150 C.-200 C. and 760- mm. of pressure in an atmosphere of nitrogen.The react-ants were vigorously agitated throughout the reaction period.This ing of the foregoing ingredients, there were then added the variousmetallic additives and in the amounts listed below. The additives werein powder form having a particle size of less than .SIL. Each of theadditivecontaining formulations were subjected to a 7-minute cure at 200C. on aluminum. The effects of such cure are reported as follows:

Table I Additive Percent Addition Cross-linking Color Adhesion Yes. YesYes.

IIIIdo.

Excellent lrjlxcellent yielded a mixture of products in which theimidazoline having the following structure predominated:

CHa(I%IT CH CH -N-CHz-OHz-NH N CH:

Imidazoline IV following structure predominated:

It will be noted that the materials which work Well are compounds ofelements in group IIB or IVA (Zinc, cadmium, mercury and lead) of theperiodic table and which can form complexes with amines or ammoniumsalts. It is interesting to note that CdO and G180; have the same eifectregardless of acid-accepting ability. Likewise, HgO and HgCl areequivalent regardless of valence state or anion. This strongly suggeststhat the action of these compounds involves the metal ion complexed withimidazoline acting on single chlorine atoms to produce stabilization andsome structure-promoting adhesion.

The properties of the zinc, cadmium, mercury, and lead compounds, incombination with the imidazoline and polymer, render them useful asaluminum adhesives;

II I

1 part of Imidazo'line I and 3 parts of epoxidized 7 soybean oil(preferably having an oxirane oxygen content between 6.5% and 7.5%) werereacted for 1 hour at 130 C. The resulting reaction product was thenmixed thoroughly with 4 parts of Geon 121 (paste grade polyvinylchloride).

general adhesives; adherent, solvent resistant sealing com- 0 pounds andadherent coatings.

EXAMPLE 2 1 part of Imidazoline I and 3 parts of epoxidized soybean oilwere prereacted for 1 hour at 130 C. The re- Into separate formulationsconsistaction product was split into three portions and compounded withthe following ingredients to prepare the designated formulations:

This example shows that addition of zinc oxide to formulations B and Cfavorably affects degradation and adhesion of imidazoline-polyvinylchloride combinations.

EXAMPLE 3 100 parts of epoxidized soybean oil, 20 parts of I midazolineII, and 100 parts of Opalon 410 were admixed and designated here asmixture A. Portions of this mixture were then compounded with varyingamounts of zinc chromate powder and cured. The specific formulations andeifects of cure are reported as follows:

Formulation (parts) Ingredient A B C D Mixture "A" an 9n on 20 Zincchromate powder. 1 9 4 8.

CURED 5 lliiNUTES A1 200 0.

Adhesion to steel Fair... Excellent- Excellent- Excellent. Adhesion toaluminum. Fair- Fair Excellent Excellent. Color 46 53 57.

(The degree of coloration bears a numerical value where white=85 andblack=0, as measured on a Photovolt Reflectometcr Model 610.)

The high molecular weight polyimidazoline of this example promotesadhesion to metal and, in combination with the chromate ion, providesexcellent water resistance for the bond to metal. These materials areparticularly useful as metal-to-metal adhesives.

The materials of each formulation were milled together at 300 F. untilsmooth, then sheeted out and pressmolded into test specimens. Cure was15 minutes at .8 380 F. Properties of the cured products were asfollows:

Formulation Tensile strength at room temp., p.s.i 7, 200 6, 900 Tensilestrength at 200 F., p.s.i 3, 500 700 Percent Creep at 250 F./60 p.s.i.load 10 The foregoing results indicate that the curing action ofirnidazolines definitely improve temperature resistance of rigidpolyvinyl chloride products. Without zinc oxide present in theimidazoline-cured product, it would degrade after several days at 200 F.The compound of formulation A, however, will not degrade for at least 6months at 220 F.

EXAMPLE 5 Cure time Time to Additive at 200 C. degrade at (minutes) 2000.

(minutes) None- 2 10 ZnO- 2 20+ CdS 2 20+ HgzS O4- 2 10 PbS 0| 2 20Prolonged testing showed that the formulation containing Pb O did notdegrade for 3 days at 200 C. This indicates that a highly stablecomposition is produced. The 'I-Ig SO formulation has limitedapplication. It is not as eifective in prolonging the usable life of theproduct at elevated temperatures. Previous experimentation has shownthat HgCl is effective in all cases and Hg SO is in some cases.Apparently the reaction of mercury compounds with imidazolines, as withammonia, is extremely complex and leads to unexpected side reactions.

The following example shows the effects of separate addition of epoxyand metal compounds versus the combined addition of such compounds to avinyl chloride copolymer.

1 Expoxidized 2ethylhexyl ester of tall oil acids. 2 Copoiymer of 97%vinyl chloride and 3% vinyl acetate.

The properties exhibited by each of the above formulations when cured atvarious periods are reflected in the following table:

halide polymer, 5 to 60 parts of a non-resinous epoxy compound which isdevoid of terminal epoxy groups, .5

Table II 4 minute cure at 200 C. 8 minute cure at 200 C. 12 minute sureat 200 C.

Formulation A B 0 A B C A B 0 Color Dark brown- Light tan-.. Tan lack*.Tan Light brown Light brown Dark brown. Flexibility Good ExcellentExcellent Poor Excellent Good G d air. Adhesion to aluminum Poor GoodFair P001 Good..." Good Fair. Crosslinking Yes Yes Yes Yes Yes Yes Yes.

*Badly degraded attendant with H01 evolution.

Formulation A shows the effect of using an epoxide to 50 parts of animidazoline and .5 to 50 parts of 2. alone in controlling degradationduring cure. Crosslinkmetallic compound which is capable of formingammonia ing was attained after 2 minutes and degradation co complexesand is a compound of a metal selected from the menced at about 4minutes. Adhesion to aluminum was group consisting of zinc, cadmium,mercury and lead. poor but adhesion to organic lacquers, such asphenolics, 2. A composition comprising 4 to 100 parts of a polywas muchimproved over a conventional plastisol. 2O meric material selected fromthe group consisting of homo- F-ormnlation B shows the improvementattained by addipolymers and copolymers of vinyl chloride, 5 to 60 partstion of zinc oxide in combination with the epoxy comof a non-resinousepoxy compound which is devoid of pound, particularly in color,flexibility and adhesion to terminal epoxy groups, .5 to 50 parts of animidazoline, aluminum. and .5 to 50 parts of a metallic compound whichis capa- Formulation C shows the effect of adding zinc oxide in ble offorming ammonia complexes and is a compound of the absence of the epoxycompound. Metal compounds a metal selected from the group consisting ofzinc, cadin the absence of epoxy compounds will enhance the mium,mercury, and lead. properties, but not as much as in the presence ofepoxy 3. A composition according to claim 1 wherein the materials. epoxycompound is selected from the group consisting of The mechanism in thisinvention is believed to involve epoxidized triglycerides of fatty oilacids; epoxidized several reactions which take place upon curing themixesters of ethenoid alcohols and saturated carboxylic acids; ture ofpolymer, imidazoline, epoxide and metallic cornepoxidized esters ofsaturated alcohols and ethenoid carpound. The initial heating ofimidazoline and polyvinyl boxylic acids; epoxidized esters of ethenoidalcohols and halide leads to formation of free radicals. These radicalsethenoid carboxylic acids; and an epoxidized olefin sein turn attack thesites of chain branching (being the lected iirom the group consisting ofmonoolefins, diolefins weakest points) of the polyvinyl halide and startextractand polymeric olefins. in-g hydrogen halide which extractionwould normally lead 4. A composition according to claim 3 wherein theimidto degradation on continued heating. The zinc, cadmium, aZolineconstitutes between about 5 to 10 parts, the metal mercury or leadcompounds become partially solubilized compound constitutes betweenabout 1 to 20 parts, and by the imidazoline on heating in the presenceof the polythe epoxy compound constitutes between about 20 to 40 mer.The metal then extracts the highly labile halogen parts. at or near thebranch site, fortifying it against attack by 5. A thermoset polymerobtained by heating the comthe free radicals produced in the initialheating step. The Position of Claim to a Curing temperaturedegradativeprocess is thus halted, allowing imidazoline 6. A composition comprising4 to 100 parts of a vinyl and free radicals 130 crosslink readily, andpreventing chloride polymer, 1 5L0 20 parts Of an imidazoline, 1 120 30degradative byproducts from exuding to the polymer surparts of ametallic compound which is capable of forming fa hi h o ld destroy anydh i b d th t may ammonia complexes and is acompound of a metal selectedhave been formed. The imidazoline, having chemically from the groupconsisting of zinc, cadmium, mercury and grafted to the polyvinyl halidecan now act as a solid wetlead, and 3 t0 100 Pants 04? an epoXidiZedfaMy Oil acid ting agent to anchor the polymer to a metal or other suI-triglycerideface to which adhesion is usually diflicult. Long chain Acomposition accord-ing to claim 6 wherein the2-substituted-2-imidazolines and l,2-disubstituted-2-imidepoxidiledtriglycefide is P i d soybean Oil. azolines are strongly polar, possesshigh surface activity A Composition Comprising 4 Parts Of p y yl 61110-d a tt a t d t many suffaces ride, 3 parts of epoxidized soybean oil, 1to 20 parts of a During the curing process, the epoxy molecules aremetallic compound which is capable of forming ammonia aft d t h i li k dolymer d become inextractcomplexes and is a compound of a metal selectedfrom the able after curing is completed, Sin th epoxy group consistingof zinc, cadmium, mercury and lead and pound is built into the polymericsystem, the polymer is 1 P of an d n endowed with permanent flexibilitywhich is desirable for A composition Comprising 20 P of a mixture manyapplications. 0 derived by admixing (a) parts of epoxidized soybean Theproportions of imidazoline, epoxide and metal com- Oil, 100 Parts Of P yy Chloride and 0 parts pound which may be added to the polymer andcopolymer of iIIlidaZOliIle and 1 l0 8 Parts Of Zinc chmmate. may varydepending upon the type of processing to be A Composition COmPTiSiIIg 90Parts of P y y used, e.g., plastis'ol, organosol, extrusion, molding,calen- Chloride, 5 Paris of epoxidized soybean 13 Parts Of dering, etc.,and the properties desired. In general, the 65 mineral filler, 5 Partsof Zinc Oxide and 2 Parts of an imidazoline may constitute between about.5 and 50, preffl oline. erably 5 to 10, parts of the final composition;the epoxy A composition comprising 3 Parts of a Product compound mayrange between about 5 to 60, preferably Obtained y reacting at for 2hours 6 Parts 20 to 40, parts; and the metal compound may range beofepoxidized soybean oil and (b) l parts of an imidaztween about .5 and50, preferably 1 to 20, parts. Curing 70 Cline, 2 Parts of Viny1chloride'dibulyl maleate P Y- of the composition is generally effectedby heating at mer and Zparts of a metallic compound which is capableabout to 225 C. for about 30 to 0.5 minutes, preferof forming ammoniacomplexes and is a compound of a ably 180 to 200 C. for about 10 to 2minutes, metal selected from the group consisting of zinc, cadmium,

We claim: mercury, and lead.

1. A composition comprising 4 to 100 parts of a vinyl 75 12. Acomposition comprising 4 parts of a vinyl chloride-vinyl acetatecopolymer, 4 parts of epoxidized Z-ethylhexyl ester of tall oil acid, 1part of zinc oxide and 2 parts of an imidazoline.

References Cited by the Examiner UNITED STATES PATENTS Gray 26045.9Waldmarm et a1. 260309 Brous 26092.8

Campbell 117132 Fikentscher 26045.9

Donia 260-92.8

Safiord 26030.6

McBrien 26045.85 Fisch et a1. 26037 Salyer et a1. 26045.7

1 2 3,002,941 10/1961 Peterson 26018 3,147,705 9/ 1964 Broderick et a1.26023 3,183,207 5/1965 Nimoy et a1 26092.8

OTHER REFERENCES Falkenburg et a1.: Oil and Soap, June 1945, pp. 143-148.

Bem'ngto-n et a1.: Journ. of Chem. 500., 1948, pp. 771- 774, London.

Zimmerman et a1.: Rubber Age, vol. 68, N0. 3, pp. 311318, December 1950.

Lee et a1.: Epoxy Resins, p. 15, McGraw-Hill Co., Inc., New York 1957.

LEON J. BERCOVITZ, Primary Examiner.

15 ALPHONSO D. SULLIVAN, MILTON STERMAN,

Examiners.

1. A COMPOSITION COMPRISING 4 TO 100 PARTS OF A VINYL HALIDE POLYMER, 5TO 60 PARTS OF A NON-RESINOUS EPOXY COMPOUND WHICH IS DEVOID OF TERMINALEPOXY GROUPS, .5 TO 50 PARTS OF AN IMIDAZOLINE AND .5 TO 50 PARTS OF AMETALLIC COMPOUND WHICH IS CAPABLE OF FORMING AMMONIA COMPLEXES AND IS ACOMPOUND OF A METAL SELECTED FROM THE GROUP CONSISTING OF ZINC, CADMIUM,MERCURY AND LEAD.